A radio frequency (RF) switch generally includes a transistor serially connected to the middle of a transmission line that forms a RF path, or a transistor connected to the middle of a transmission line in shunt. The RF switch connects or disconnects a RF path by controlling ON and OFF states of a transistor using bias of the transistor.
FIGS. 1 and 2 show RF switches according to the related art. Hereinafter a RF switch according to the related art will be described with reference to FIGS. 1 and 2.
FIG. 1 is a RF switch having a field effect transistor (FET) connected to ground in shunt.
As shown in FIG. 1, the RF switch according to the related art includes a transistor Q1 12 connected to a RF transmission line 11 in shunt, a resistor R1 13 connected to a gate terminal of the transistor Q1 12, and a gate control voltage input terminal VG 14 connected to the resistor R1 13. A source terminal of the transistor Q1 12 is grounded. As described above, the RF switch according to the related art connects or disconnects the RF transmission line by opening or closing the transistor using bias of the transistor Q1 12.
The maximum power of the RF switch of FIG. 1 is decided according to a size of the transistor. Therefore, the bigger transistor must be used so that the switch could handle the greater RF power. In this case, the isolation performance of the RF switch may deteriorate.
The RF switch according to the related art has been known as that the isolation performance thereof is decided based on unique characteristics of a transistor and that the isolation performance thereof is constant regardless of frequency increment. However, the RF switch according to the related art was not embodied using only one shunt transistor because the isolation of a shunt transistor is not high enough.
FIG. 2 is a diagram illustrating a RF switch using a serially-connected field effect transistor (FET) according to the related art.
As shown in FIG. 2, the RF switch according to the related art includes a field effect transistor (FET) Q1 21 serially connected to a RF transmission line, a resistor R1 23 connected to a gate terminal of the FET 21, and a gate control voltage input terminal VG1 22.
The RF switch according to the related art connects or disconnects the RF transmission path by opening or closing the transistor using bias of the transistor, as shown in FIG. 2.
In the RF switch according to the related art shown in FIG. 2, the isolation performance of the transistor is decided according to unique characteristic of the transistor, and the isolation performance abruptly decreases according to frequency increment. Also, the RF switch according to the related art provides about 20 dB of isolation performance at 3 GHz. However, the isolation performance of the RF switch according to the related art is not enough at a disconnecting state of the RF switch.